The present invention relates to a suction box for a system for conveying flat media in a printing machine for flat media. The invention relates to a system for conveying flat media comprising at least one suction box. The invention also relates to a printing machine for flat media, equipped with a system for conveying flat media, and the system comprising at least one suction box.
A printing machine is used in the packaging industry for printing flat media such as sheets or a web of paper or cardboard. The machine comprises several stations in succession. A first infeed station, situated furthest upstream, inputs the medium in succession. The infeed station supplies several printing stations, in the form of one or more printing units placed one after the other. Each printing unit prints a specific color using an ink which has the equivalent coloration. The machine can easily accept different sizes of medium. A delivery station which collects the medium which has been printed with an image is provided at the end of the machine.
In the case of printing sheets of cardboard, particularly corrugated cardboard, the technology used most frequently is flexography using a flexo unit. Digital printing is also developing, with the use of printing units equipped with digital print heads, for example of the inkjet-type. This printing technology enables the packaging manufacturer to change print jobs very quickly in order to print new sheets from a computer file representing the packaging.
The printing machine comprises one or more printing units with the number of units depending on the number of colors desired. The medium is moved longitudinally from upstream to downstream from the infeed station, to the printing units and as far as the delivery station. In order to obtain a final high-quality image on the printed medium, it is in particular necessary that all the printed dots of different colors be placed exactly next to one another. It is also necessary that the printed dots not be deformed.
The printing quality obtained on the flat medium depends not only on the quality of the printing machines, the quality of the inks used and the quality of the media input, but also on the quality and accuracy of the conveying system or systems used.
The medium is conveyed by a vacuum conveying system using a belt, flat straps, or steel rolls driven in order to move the medium longitudinally from one printing unit to another, upstream to downstream, from the infeed station to the delivery station. In order to obtain optimal print quality, one of the fundamental principles is that the medium is conveyed at a speed which is as uniform as possible. Another principle is that the medium must be held as firmly as possible and must be guided perfectly by the conveying system so that there is no deviation during the printing by the printing unit or units or between the printing unit or units.